Effects of the SW Atlantic burrowing crab Chasmagnathus granulata on a Spartina salt marsh

Abstract

In this work we evaluated the effect of the burrowing crab Chasmagnathus granulata on the soil quality and on the cordgrass Spartina densiflora in a SW Atlantic coastal lagoon (Argentina, 37'32'S, 57" 19'W). Soil hardness and percolation rates were higher outside the crab inhabited area than inside, and soil profiles showed 2 different strata In areas without crabs. Crabs were associated with low soil water content, a higher variabihty In pH, and a homogeneous distribution of organic matter. Meiofaunal abundance was lower inside the area inhabited by crabs than outside. The water content of aboveground structures of S. densiflora was lower inside the crab populated areas. Leaf survival was lower inside the area inhabited by crabs than outside. In areas with new shoots (after burning by a brush flre) crabs depleted the aboveground plant structures. A caging experiment showed that crabs decreased leaf survival by herbivory. During the experiment, substrata was covered by sediment displaced by crabs, and the area showed less soil hardness and lower percolation rates than controls. Crabs decreased water content and organic matter on upper sediment layers. Meiofaunal abundance (arachnids and insects) was higher in control plots (without crabs) than in treatment plots. A field selection expenment showed that crabs decreased survival of young stems, but did not affect old stems. K11 this evidence suggests that C. granulata affects cordgrass production by herbivory on new shoots, and can change the physical characteristics of the environment, which may also indirectly affect S. densiflora production. Thus, the general belief that in Spartina marshes only a small proportion of primary production is consumed in situ may not apply to SW Atlantic Spartina marshes inhabited by crabs.

A trophic cascade regulates salt marsh primary production

“…These results have important conservation implications and suggest that the overexploitation of a major predator may indirectly alter the structure and function of intertidal marsh habitats. In addition, our findings, combined with mounting evidence showing grazer control of plant growth in Argentine (31) and Canadian (32) marshes, suggest that the current paradigm in salt marsh ecology, and the application of this paradigm to other systems, needs to be reevaluated.…”

The effect of the SW Atlantic burrowing crab Chasmagnathus granulatus on the intertidal razor clam Tagelus plebeius

“…Consequently, there are distinct changes in sediment chemistry (Gutiérrez et al, 2006), composition and transport (e.g., Palomo et al, 2004) and in bottom topography (Escapa et al, 2004;Perillo and Iribarne, 2004) within crab beds. These changes directly affect abundances of nematodes, polychaetes, juvenile crabs Palomo et al, 2004;Escapa et al, 2004), the fiddler crab Uca uruguayensis (Daleo et al, 2003), the mud crab Cyrtograpsus angulatus , the cordgrass Spartina densiflora (Bortolus and Iribarne, 1999;Bortolus et al, 2002Bortolus et al, , 2004, the pickleweed Sarcocornia perennis (formerly known as Salicornia ambigua; Perillo and Iribarne, 2004) and indirectly habitat use and foraging rates of migratory shorebirds Palomo et al, 2003;Iribarne et al, 2005).…”

“…The crab excavates and maintains semi-permanent open burrows (Spivak et al, 1994;Iribarne et al, 1997). In salt marshes these burrows are straight tunnels (entrance diameter up to 10 cm) that may extend down to 1 m depth (Iribarne et al, 1997;Bortolus and Iribarne, 1999;Bortolus et al, 2004;Botto et al, 2005). In mud flats, tidal creeks and channels, where crabs are mainly deposit feeding, burrows are shallow (down to 30 cm depth) and with funnel-shaped entrances (diameter up to 20 cm; Iribarne et al, 1997;Botto et al, 2005).…”

“…This species (up to 4 cm carapace width) inhabits tidal flats and salt marshes dominated by Spartina spp. and Sarcocornia spp., with densities up to 60 crabs m − 2 (Iribarne et al, 1997;Bortolus and Iribarne, 1999). The crab excavates and maintains semi-permanent open burrows (Spivak et al, 1994;Iribarne et al, 1997).…”

Combined impact of ultraviolet radiation and increased nutrients supply: a test of the potential anthropogenic impacts on the benthic amphipod Amphitoe valida from Patagonian waters (Argentina)

“…There is a high amount of evidence that herbivores can regulate vegetal populations by top-down control (i.e., invertebrates, Bortolus and Iribarne, 1999;fish, Burkepile and Hay, 2010). Based on our results on FCR, it seems reasonable to conclude that, in a scenario of eutrophication (as a result of anthropogenic activities) and high solar UVR levels, an increase in macroalgae food quality as a result of high nutrient inputs, could favor only males of A. valida, by reducing the negative effects of UVR on their FCR.…”